Computer disk drives and other applications commonly use multiplexers. A multiplexer is a device that allows two or more signals to be transmitted simultaneously on a single communication channel. Other multiplexer switch the output channel between the input channels. Generally, multiplexers with more channels requires more time to switch between channels. Because the speed of a multiplexer determines the rate of transmission of the multiplexed data, it is desirable to have a faster multiplexer.
Hard disk drives typically include one or more rotating magnetic platters encased within a environmentally controlled housing which further includes all of the electronics and mechanics to read and write data and interface with other devices. Read/write heads are positioned above each of the platters, and typically on each face, to record and read data. The electronics of a hard disk drive are coupled with the read/write heads and include numerous components to control the position of the heads and generate or sense the electromagnetic fields representing data. The components receive data from a host device, such as a personal computer, and translate that data into magnetic encodings that are written onto the disk platters by the heads. Further, when a host device requests data from the drive, the electronics locates the desired data, senses the magnetic encodings which represent that data and translates those encodings back into the binary digital information which the host device can understand. Further, error detection and correction algorithms are applied to ensure accurate storage and retrieval of data.
One area in which significant advancements have been made has been in the area of read/write head technology and the methods of interpreting the magnetic fluctuations sensed by these heads. The read/write head, of which a typical hard disk has several, is the interface between magnetic platters and the disk drive electronics. The read/write head actually reads and writes the magnetically encoded data as areas of magnetic flux on the platters. Data, consisting of binary 1""s and 0""s, are encoded by sequences of the presence or absence of flux reversals recorded or detected by the read/write head. A flux reversal is a change in the magnetic flux in two contiguous areas of the disk platter. Traditional hard drives read data off the platters by detecting the voltage peak imparted in the read/write head when a flux reversal passes underneath the read/write head as the platter rotate. This is known as xe2x80x9cpeak detection.xe2x80x9d However, increasing storage densities require reduced peak amplitudes and better signal discrimination and higher platter rotational speeds are pushing the peaks closer together making peak detection more difficult to accomplish.
Magneto-resistive (xe2x80x9cMRxe2x80x9d) read/write heads have been developed with increased sensitivity to sense smaller amplitude magnetic signals and with increased signal discrimination to address some of the problems with increasing storage densities. In addition, another technology, known as Partial Response Maximum Likelihood (xe2x80x9cPRMLxe2x80x9d), has been developed to further address the problems with peak detection as densities and rotational speeds increase. PRML is an algorithm implemented in the disk drive electronics to interpret the magnetic signals sensed by the read/write heads. PRML based disk drives read the analog waveforms generated by the magnetic flux reversals stored on the disk. However, instead of looking for peak values to indicate flux reversals, PRML based drives digitally sample this analog waveform (the xe2x80x9cPartial Responsexe2x80x9d) and use advanced signal processing technologies to determine the bit pattern represented by that wave form (the xe2x80x9cMaximum Likelihoodxe2x80x9d). PRML technology, in conjunction magneto-resistive (xe2x80x9cMRxe2x80x9d) heads, have permitted manufacturers to further increase data storage densities. PRML technology further tolerates more noise in the sensed magnetic signals permitting the use of lower quality platters and read/write heads which increases manufacturing yields and lowers costs.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below relate to
A high-speed multiplexer that includes a reduced number of components in the pull-up and/or the pull-down circuits operates faster than conventional multiplexers and can process higher frequency input signals. The pull-up circuit may be a singe p-type MOSFET transistor and the pull-down circuit may be a single n-type MOSFET transistor. The switching circuits may include transistor-based NOR gates. The multiplexer may have numerous channels, for example 2 to 256 or more channels.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.